Bulkhead fittings are used as part of a conduit system to pass a conduit, tube, or other similar apparatus through a fluid-impermeable barrier or bulkhead and maintain the integrity of the barrier. These barriers or bulkheads may be employed to form fuel tanks, climate-controlled spaces, air containment units, and other enclosures intended to segregate either a liquid or a gas from a surrounding environment. These bulkhead fittings are furnished with redundant seals to prevent external fluid transfer or leakage through the bulkhead around the tube by means of O-rings, fay, and fillet seals.
A bulkhead fitting traditionally functions by providing a robust and reliable connection to structure allowing fluid to be transmitted across the interface through a transport element tube. In hydraulic systems, the hydraulic fluid (and therefore hydraulic transfer element tube) may become heated to high temperatures. Such high temperatures may damage bulkhead, barrier, or other surrounding structure if there is a direct connection between the transfer element tube and the heat-sensitive structure. Heat may also deform or modify the interface between the bulkhead and conduit and compromise the sealing features of the fitting. Therefore, bulkhead fittings have been developed that thermally insulate the fitting and connected conduit from a bulkhead on which the fitting is mounted to prevent thermal damage to the bulkhead.
One example of such thermal insulation is the use of a plastic insulator between the fitting and bulkhead. This barrier may be up to an inch thick on either side of the fitting in order to provide sufficient insulation to prevent damage to the bulkhead. Another example is to provide a fitting with a wide, thermally conductive surface to dissipate heat without creating a localized area of high temperature.
With the use of composite materials for aircraft, it may be necessary to utilize hydraulic conduits to transfer electrical energy from lightning strikes, precipitation static, and other electromagnetic events (EME). Because thermal insulating materials also tend to be electrically insulating, such structures may not allow a combined solution of thermal non-conductivity (to resist the flow of heat) and electrical conductivity (to pass the flow of electrical current from fitting to bulkhead) in the properties of the insulating materials in a hydraulic bulkhead fitting. To provide for electrical conductivity while providing thermal insulation, electric current may be diverted away from the hydraulic line.
Further, Federal Aviation Regulation (FAR) 25.981 requires a redundant system so that any single failure combined with a latent failure cannot result in an ignition source within the fuel tank of an aircraft. There is therefore recognized a need in the art for an improved bulkhead fitting assembly that satisfies FAR 25.981.
One method of overcoming this restriction has been the use of additional components included with a bulkhead fitting installation. However, installing these additional parts can add time and weight to a bulkhead fitting installation to provide for protection against spark propagation. There is therefore a need for a bulkhead fitting assembly that addresses the aforementioned shortcomings and others that may exist in prior art devices.